Embarrassing question but what is it called when you feel tense and sexually aroused without a sexual partner and you have to masturbate to orgasm to feel better ??

It's called normal: There is nothing wrong with this. Virtually all humans have feelings like this from time to time. There's nothing wrong or abnormal about it. "What is it called?" Nothing: there is no name for this. The only problem might arise if these feelings are very frequent (e.g. a few times every day) and are interfering with your life. In that case, discuss with your doctor.